1. Field of the Invention
The present invention relates to an improvement of a control apparatus for a drive system of a hybrid vehicle.
2. Description of Related Art
There is known a hybrid vehicle drive system including: a drive system of a hybrid vehicle including: a first differential mechanism provided with a rotary element connected to an engine and a rotary element connected to a first electric motor; a second differential mechanism provided with a rotary element connected to a second electric motor and a rotary element connected to an output rotary member; a brake configured to selectively fix another rotary elements of the second differential mechanism to a stationary member; and a clutch configured to selectively connect the rotary element of the first differential mechanism connected to the engine and the above-indicated another rotary element of the second differential mechanism. Regarding such a hybrid vehicle drive system, techniques for starting the engine have been proposed. JP-2013-133101 A1 discloses an example of such techniques, wherein EV controls of the drive system are implemented so as to improve fuel economy of the hybrid vehicle. According to this technique, the second electric motor is operated to generate a reaction force while the first electric motor is operated to generate a torque to raise an operating speed of the engine, in an engaged state of the brake and in a released state of the clutch, or in a released state of the brake and in an engaged state of the clutch.
According to the prior art techniques described above, however, there is a risk of failure to start the engine while an output of a battery is insufficient, as in a cold state of the engine, so that a sufficiently large amount of electric energy cannot be supplied to the first and second electric motors. This problem was first discovered by the inventor of the present invention in the process of an intensive study in an effort to improve the performance of the hybrid vehicle.